POS0891 REUMA.pt/MYOSITIS – THE PORTUGUESE REGISTRY OF INFLAMMATORY MYOPATHIES
Authors: E. Dourado, A. T. Melo, P. Martins, M. J. Sousa Bandeira, V. Fraga, J. L. Ferraro, A. Saraiva, M. Sousa, H. Parente, C. Dantas Soares, A. M. Gomes Correia, D. Esperança Almeida, S. P. Dinis, A. S. Pinto, F. Oliveira Pinheiro, M. Rato, T. Beirão, B. Samões, B. Santos, C. Mazeda, A. Chícharo, M. Faria, A. Neto, M. H. Fernandes Lourenco, L. Brites, M. Rodrigues, J. Silva-Dinis, J. Madruga Dias, F. Araújo, N. F. Martins, M. Couto, A. Valido, M. J. Santos, S. C. Barreira, J. E. Fonseca, R. Campanilho-Marques
Journal: Annals of the Rheumatic Diseases (2022)

Background The idiopathic inflammatory myopathies (IMM) module of the Rheumatic Diseases Portuguese Register (Reuma.pt/Myositis) is a tool used to systematically evaluate IIM patients. Objectives To clinically characterise the Reuma.pt/Myositis cohort. Methods Multicentre open cohort study, including IIM patients registered in Reuma.pt up to January 2022. Data collected included demographic, clinical, and treatment data and patient-reported outcomes. Data were presented as frequencies and median (interquartile range) for categorical and continuous variables, respectively. Results 280 patients were included, 71.4% female, 89.4% Caucasian, with a median age at diagnosis and disease duration of 48.9 (33.6-59.3) and 5.3 (3.0-9.8) years, respectively. Patients were classified as having definite (N=57/118, 48.3%; N=35/224, 15.6%), likely (N=23/118, 19.5%; N=50/224, 22.3%), or possible (N=2/118, 1.7%; N=46/224, 20.5%) IIM by 2017 EULAR/ACR and Bohan-Peter criteria, respectively. Disease subtypes included dermatomyositis (DM, N=122/280, 43.6%), polymyositis (N=59/280, 21.1%), myositis in overlap syndromes (N=41/280, 14.6%), clinically amyopathic DM (N=17/280, 6.1%), nonspecific myositis (N=13/280, 4.6%), mixed connective tissue disease (N=12/280, 4.3%), immune-mediated necrotizing myositis (N=9/280, 3.2%), and inclusion bodies myopathy (N=7/280, 2.5%). Over the course of the disease, the most common symptoms were proximal muscle weakness (N=180/215, 83.7%), arthralgia (N=127/249, 52.9%), erythema (N=63/166, 38.0%), fatigue (N=47/127, 37.0%), Raynaud’s phenomenon (N=76/234, 32.5%), and dysphagia (N=33/121, 27.3%), and the most common clinical signs were Gottron’s sign (N=75/184, 40.8%), heliotrope rash (N=101/252, 40.1%), Gottron’s papules (N=93/237, 39.2%), and arthritis (N=38/98, 38.8%). Organ involvement included lung (N=78/230, 33.9%), oesophageal (N=40/221, 18.1%), and heart (N=11/229, 4.8%) involvements. Most patients expressed myositis-specific (MSA, N=158/242, 65.3%) and/or myositis-associated (MAA, 112/242, 46.3%) antibodies. The most frequent antibodies were anti-SSA/SSB (N=70/231, 30.3%), anti-Jo1 (N=56/236, 23.7%), and anti-Mi2 (N=31/212, 14.6%). Most patients had a myopathic pattern on electromyogram (N=101/138, 73.2%), muscle oedema in magnetic resonance (N=33/62, 53.2%), and high CK (N=154/200, 55.0%) and aldolase levels (N=74/135, 54.8%) at diagnosis, with median highest CK levels of 1308 (518-3172) and aldolase of 42 (12-121) mg/dL. Neoplasia was found in 11/127 patients (8.7%), most commonly breast (N=3/11, 27.3%), non-melanoma skin (N=2/11, 18.2%), and colorectal (N=2/11, 18.2%) cancer (Table 1). Most patients with cancer-associated myositis had DM (N=8/11, 72.7%) and expressed MSA (N=6/11) and/or MAA (N=3/11). The most used drugs over the course of disease were glucocorticoids (N=201/280, 71.8%), methotrexate (N=117/280, 41.8%), hydroxychloroquine (N=87/280, 31.1%), azathioprine (N=85/280, 30.4%), mycophenolate mofetil (N=56/280, 20.0%), intravenous immunoglobulin (N=55/280, 19.6%), and rituximab (N=45/280, 16.1%). At the last follow-up, there was a median MMT8 of 150 (142-150), modified DAS skin of 0 (0-1), global VAS of 10 (0-50) mm, and HAQ of 0.125 (0.000-1.125). Table 1. Autoantibodies in cancer-associated myositis Cancer IIM Autoantibodies Breast DM (3) Mi2, SRP (+ SSA/SSB), Pm/Scl Skin (non-melanoma) Clinically amyopathic DM, PM Jo1, SAE1 (+SSA/SSB) Colorectal DM (2) Mi2 (2) Kidney DM - Lung DM - Lymphoma Inclusion bodies myopathy - Unknown DM - Conclusion Reuma.pt/Myositis adequately captures the main features of inflammatory myopathies’ patients, depicting in this first report a heterogeneous population, with frequent muscle, joint, skin and lung involvements. Of interest, most patients reached low disease activity at the last follow-up appointment. Disclosure of Interests None declared